1. Field of the Invention
The invention relates to a bidirectional optical amplifier having a first and second direction separator with a first and second amplifier path and feed devices for inputting pump signals.
2. Description of the Related Art
Optical amplifiers are required for optical transmission systems in which data signals are transmitted bidirectionally via one fiber.
Various bidirectional optical fiber amplifiers are described in xe2x80x9cErbium-Doped Fiber Amplifiersxe2x80x9d by Emmanuel Desurvire, Verlag John Wiley and Sons, Inc. NY, 1994, pages 462 to 465. In order to pump a fiber amplifier in the direction of the data signal (FIG. 6.7), the fiber amplifier is preceded by a selective-wavelength coupler. However, this results in the noise response becoming worse due to attenuation of the user signal. In another variant (page 465, FIG. 6.8), pumping is carried out in the opposite direction to the signal direction, which once again fundamentally leads to poorer signal-to-noise ratios since a pump signal which has been attenuated by the amplifier fiber is present at the amplifier input.
The object of the invention is thus to specify a bidirectional amplifier with an improved signal-to-noise ratio.
This object is achieved by a bidirectional amplifier comprising a first direction separator having a first, second, and third connection, to whose first connection a first fiber section is connected; a second direction separator having a first, second, and third connection, to whose first connection a second fiber section of the transmission fibers is connected; a first fiber amplifier; a second fiber amplifier; a first amplifier path, comprising the first fiber amplifier arranged between the second connection of the first direction separator and the third connection of the second direction separator, the first fiber amplifier amplifying a first optical user signal which is supplied to the first connection of the first direction separator and which is then fed in via the first connection of the second direction separator to the second fiber section; and a first feed device for inputting pump signals that follow the first fiber amplifier, the first feed device having an output that is connected to the third connection of the second direction separator, the second fiber amplifier being pumped in a signal direction via the second direction separator that is connected to the first feed device output, the bidirectional amplifier further comprising a second amplifier path, comprising the second fiber amplifier arranged between the second connection of the second direction separator and the third connection of the first direction separator, the second fiber amplifier amplifying a second optical user signal, which is supplied to the first connection of the second direction separator and is then fed to the first fiber section via the first direction separator; and a second feed device for inputting pump signals that follow the second fiber amplifier, the second feed device having an output that is connected to the third connection of the first direction separator; the first fiber amplifier being pumped in a signal direction via the first direction separator that is connected to the second feed device output; and the second fiber amplifier being pumped in a signal direction via the second direction separator that is connected to the first feed device output.
In this embodiment, the first and second direction separators may be configured as filters such that each respective pump signal, rather than amplified optical user signals, are fed into the second and the first amplifier path respectively. Also, the feed devices may be wavelength multiplexers.
In another embodiment of the invention, the bidirectional amplifier may comprise a first four-port direction separator having a first, second, third, and fourth connection, the first connection being connected to a first fiber section; a second four-port direction separator having a first, second, third, and fourth connection, the first connection being connected to a second fiber section; a first fiber amplifier, which is arranged between the second connection of the first four-port direction separator and the third connection of the second four-port direction separator and amplifies a first optical user signal which is supplied to the first connection of the first four-port direction separator and is then fed via the first connection of the second four-port direction separator to the second fiber section; a second fiber amplifier, which is arranged between the second connection of the second four-port direction separator and the third connection of the first four-port direction separator and amplifies a second optical user signal which is supplied to the first connection of the second four-port direction separator and is then fed via the first connection of the first four-port direction separator to the first fiber section; a first pump signal being fed into the fourth connection of the first four-port direction separator, the first pump signal being coupled to the first fiber amplifier in a direction of the first optical user signal and transmitted in a signal direction; and a second pump signal being fed into the fourth connection of the second four-port direction separator, the second pump signal being coupled to the second fiber amplifier in a direction of the second optical user signal and transmitted in a signal direction.
In this other embodiment, the first and second four-port direction separators may be based on beam splitter principles and the pump signals in each case pump the respective fiber amplifiers in a direction of each respective optical data signal. In either embodiment, the fiber amplifiers may also be pumped in an opposite direction to a transmission direction of respective optical user signals.
An improvement in the noise response is achieved if the optical user signal and pump signal are propagated in the same direction and there are no feed devices for the respective pump signal to cause additional attenuation of the input user signals to the fiber amplifiers.